The wireless local-area network (WLAN) technology known as “Wi-Fi” has been standardized by IEEE in the 802.11 series of specifications (i.e., as “IEEE Standard for Information technology—Telecommunications and information exchange between systems. Local and metropolitan area networks—Specific requirements. Part 11: Wireless LAN Medium Access Control (MAC) and Physical Layer (PHY) Specifications”).
The IEEE 802.11 specifications regulate the functions and operations of the Wi-Fi access points (APs) or wireless terminals, collectively known as “stations” or “STA,” in the IEEE 802.11, including the physical layer protocols, Medium Access Control (MAC) layer protocols, and other aspects needed to secure compatibility and inter-operability between access points and portable terminals. Wi-Fi is commonly used as wireless extensions to fixed broadband access, e.g., in domestic environments and in so-called hotspots, like airports, train stations and restaurants.
Recently, Wi-Fi has been subject to increased interest from cellular network operators, who are studying the possibility of using Wi-Fi for purposes beyond its conventional role as an extension to fixed broadband access. These operators are responding to the ever-increasing market demands for wireless bandwidth, and are interested in using Wi-Fi technology as an extension of, or alternative to, cellular radio access network technologies (RATs). Network operators that are currently serving mobile users with, for example, any of the technologies standardized by the 3rd-Generation Partnership Project (3GPP), including the radio-access technologies known as Long-Term Evolution (LTE), Universal Mobile Telecommunications System (UMTS)/Wideband Code-Division Multiple Access (WCDMA), and Global System for Mobile Communications (GSM), see Wi-Fi as a wireless technology that can provide good additional support for users in their regular cellular networks.
There is currently quite intense activity in the area of operator-controlled Wi-Fi in several standardisation organisations. In 3GPP, activities to connect Wi-Fi access points (APs) to the 3GPP-specified core network are being pursued, and in the Wi-Fi Alliance (WFA), activities related to certification of Wi-Fi products are being undertaken, which to some extent also is driven from the need to make Wi-Fi a viable wireless technology for cellular operators to support high bandwidth offerings in their networks. The term Wi-Fi offload is commonly used and points towards that cellular network operators seek means to offload traffic from their cellular networks to Wi-Fi, e.g. in peak-traffic-hours and in situations when the cellular network for one reason or another needs to be off-loaded, e.g. to provide requested quality of service, maximise bandwidth or simply for coverage.
For a network operator, offering a mix of two technologies that are standardised in isolation from each other provides a challenge of providing intelligent mechanisms for co-existence. One such area is connection management.
Portable wireless devices or terminal devices (also referred to in 3GPP as UEs) today usually support both Wi-Fi and a number of 3GPP cellular technologies, but many of the terminal devices are effectively behaving as two separate devices, from a radio access perspective. The 3GPP radio access network (RAN) and the modems and protocols that are operating pursuant to the 3GPP specifications are basically unaware of the wireless access Wi-Fi protocols and modems that are operating pursuant to the 802.11 specifications.
One solution for performing traffic steering between a WLAN and a 3GPP network is presented below. This option allows a first RAT, e.g. a 3GPP RAT, to control the connection of a terminal device to a second RAT, e.g. a WLAN, by sending traffic steering commands ordering the terminal device to steer traffic from/to the second RAT. The following is based on section 6.1.3 of 3GPP TR 37.834 v12.0.0 (2013-12) and corresponds to ‘Solution 3’ in that document.
In this solution the traffic steering for UEs in RRC CONNECTED/CELL_DCH state is controlled by the network using dedicated traffic steering commands, potentially based also on WLAN measurements (reported by the UE).
For UEs in IDLE mode and CELL_FACH, CELL_PCH and URA_PCH states the solution is similar to the solutions described in sections 6.1.1 and 6.1.2 of 3GPP TR 37.834 v12.0.0 (2013-12). Alternatively, UEs in those RRC (radio resource control) states can be configured to connect to RAN and wait for dedicated traffic steering commands.
User preference always takes precedence over RAN based or Access network discovery and selection function (ANDSF) based rules (e.g. when a non-operator WLAN is preferred or WLAN is off).
In this solution:                if ANDSF is not present, the UE moves the traffic indicated in the steering command to WLAN or 3GPP as indicated;        when multiple Access Networks are possible according to the ANDSF policy, the traffic steering commands can override order of access network priorities, e.g. if for certain IP flows ANDSF indicates a prioritized order of 3GPP access and WLAN, upon reception of a command to steer traffic from 3GPP access to WLAN, the UE moves the corresponding flows to WLAN;        The dedicated traffic steering command cannot override ANDSF in other cases i.e. the UE shall not consider an access network that is forbidden by ANDSF as being available based on the steering command. The UE should not consider an access network that is restricted by ANDSF as being available based on the steering command.        
The above rules apply whether the H-ANDSF (Home-ANDSF) or the V-ANDSF (Visiting-ANDSF) policy are active.
As an example, traffic steering for UEs in RRC CONNECTED/CELL_DCH comprises the steps shown in FIG. 1.
Step 1. Measurement control: The eNB/RNC (radio network controller) configures the UE measurement procedures including the identity of the target WLAN to be measured.
Step 2. Measurement report: The UE is triggered to send MEASUREMENT REPORT by the rules set by the measurement control.
Step 3. Traffic steering: The eNB/RNC sends the steering command message to the UE to perform the traffic steering based on the reported measurements and loading in the RAN.
It will be noted that the above procedures do not take into account user preference and/or the WLAN radio state. For example, based on user preferences and/or WLAN radio state, a UE may not be able to perform the configured measurement events. Additionally, the procedures need to allow a UE to be able to prioritize non-operator WLAN over operator WLAN. For example, the UE may disassociate from the operator WLAN and associate with the higher priority non-operator WLAN at any time during the measurement process.
The procedure illustrated above, and the following description can apply to UMTS CELL_FACH as well. The procedure can also be extended to UMTS/LTE Idle modes and UMTS CELL/URA_PCH states, e.g. UEs may be configured to report some indication (e.g. on available WLAN measurements) in a RRC UL (uplink) message, e.g., RRC connection request (from Idle, in UMTS/LTE) or CELL UPDATE (in UMTS CELL/URA_PCH states).
It should be noted that some of the steps above, e.g. steps 1&2, can be optional, based on the RAN/UE configuration.
Step 1: Measurement Control
For measurement control, the following examples are types of information that the UE can be configured to measure on the operator WLAN:
1. Measurement events to trigger reporting as defined in Table 1 below
2. Target identification as defined in Table 2 below
3. Measurements to report as defined in Table 3 below
Based on the measurement events defined in TS 36.331 and TS 25.331, Table 1 shows the candidate measurement events for WLAN:
TABLE 1EventDescriptionW1WLAN becomes better than a threshold (to trigger traffic steeringto WLAN)W2WLAN becomes worse than a threshold (to trigger traffic steeringfrom WLAN)W33GPP Cell's radio quality becomes worse than threshold1 andWLAN's radio quality becomes better than threshold2 (to triggertraffic steering to WLAN)W4WLAN's radio quality becomes worse than threshold1 and 3GPPCell's radio quality becomes better than threshold2 (to triggertraffic steering from WLAN)
It should be noted that the thresholds are based on the values of the measurements to report defined in Table 3.
The target identification is used to indicate to the UE which WLAN to consider for the measurement control procedures including the target WLAN ID and the operating channels to search for. Table 2 shows the candidate target identifiers for WLAN.
It should be noted that for steering traffic from WLAN, i.e., W2/W4, it may be sufficient that just the serving WLAN below a threshold is reported, i.e. the WLAN target identifiers are not needed.
TABLE 2AvailabilityIdentifierDescriptionin WLANBSSIDBasic Service Set Identifier: ForBeacon orinfrastructure BSS, the BSSID is the MACProbeaddress of the wireless access pointResponseSSIDService Set Identifier: The SSID can beBeacon orused in multiple, possibly overlapping,ProbeBSSsResponseHESSIDHomogeneous Extended Service Set Identifier:Beacon orA MAC address whose value shall beProbeconfigured by the Hotspot Operator with theResponsesame value as the BSSID of one of the APs(802.11)in the network. All APs in the wireless networkshall be configured with the same HESSIDvalue.DomainDomain Name List element provides a list ofANQPName Listone or more domain names of the entity(HS 2.0)operating the WLAN access network.OperatingIndication of the target WLAN frequency.N/Aclass,See Annex E of 802.11 [5] for definitionschannelof the different operating classesnumberNOTE:If above information is not available in eNB/RNC, it is possible for RAN to configure general WLAN measurementsStep 2: Measurement Report
Table 3 shows the candidate measurements to report for WLAN.
TABLE 3AvailabilityIdentifierDescriptionin WLANRCPIReceived Channel Power Indicator:MeasurementMeasure of the received RF powerin the selected channel for a receivedframe in the range of −110 to 0 dBmRSNIReceived Signal to Noise Indicator:MeasurementAn indication of the signal to noiseplus interference ratio of a receivedIEEE 802.11 frame. Defined by the ratioof the received signal power (RCPI-ANPI)to the noise plus interference power(ANPI) in steps of 0.5 dB in the rangefrom −10 dB to +117 dBBSS LoadContains information on the current STABeacon orpopulation and traffic levels in the BSS.Probe Response(802.11k)WANIncludes estimates of DL and UL speedsANQP (HS 2.0)metricsand loading as well as link status andwhether the WLAN AP is at capacity.Step 3: Traffic Steering
In order for RAN to control traffic routing (if agreed to be supported) if ANDSF is not used, the RAN would need to know which Access Point Names (APNs)/bearers may be (not) offloaded. The RAN also needs means to inform the UEs accordingly so that e.g. the UE can issue the corresponding binding update with the CN (core network) over S2c. This would impact signalling between CN and eNB as well as the UE behaviour between AS (Access stratum) and NAS (Non-access stratum) level.
Table 4 shows candidate examples for identifying the traffic to steer to or from WLAN.
TABLE 4IdentifierDescriptionDRB/RB-IDIdentity of a radio bearerQCIQoS Class Identifier
In LTE, an RRM (radio resource management) measurement framework exists according to which an eNB can configure the UE to report to the network when the UE finds an LTE cell which has e.g. a signal strength above a configured threshold. The UE would, when configured with such a configuration, scan for LTE cells and if the UE finds an LTE cell with a signal strength above the configured threshold, a measurement report would be triggered.
The UE includes in this report measurements also for other cells, even those cells which do not have a signal strength above the threshold.
The eNB uses these measurements to perform mobility procedures for the UE, e.g. to add additional cells for the UE to boost the UE's throughput.
To further improve the performance of LTE systems, 3GPP has started a study on how to enable the use of LTE in unlicensed spectrum, which is referred to as Licensed Assisted Access (LAA). As unlicensed spectrum can never match the qualities of licensed spectrum, the intention with LAA is to apply carrier aggregation and use a secondary carrier in an unlicensed band, while having a primary carrier in a licensed band. A carrier used in unlicensed bands will herein be referred to as an LAA-carrier/LAA-cell/etc.
When LTE is operating in unlicensed spectrum there may be multiple operators which have LAA cells in the same band. This is different from normal LTE operation where the operator has dedicated spectrum and other operators are not allowed to deploy cells on the same frequency.